The present invention relates to an efficient room lighting fixture with safe and effective air sterilization, and finds particular application in public spaces such as hospitals, health care institutions, dormitories, schools and offices.
Short wave ultra violet (UV-C) energy has long been used for air sterilization. The usefulness of UV-C irradiation on air quality lies in the effect on germs (microorganisms) transmitted in aerosolized form. Such infectious germs are generally less than 0.3 microns in diameter and are suspended or “float” in the air.
Different types of microorganisms vary significantly in their resistance to W-C irradiation. For example, spores such as anthrax have a “cell wall” (like bacteria) as well as an outer “shell” which must be penetrated by the W-C energy. Viruses such as influenza, the common cold, SARS, measles and small pox do not have a cell wall and are about five times more susceptible to W-C radiation than spores. Bacteria with a cell wall such as tuberculosis, even extended drug resistant (XDR) TB, may be ten times more vulnerable to W-C radiation than anthrax spores. The W-C “dose” needed to destroy germs is generally expressed as joules (one W-C watt of energy for one second) per square meter; or the equivalent μJ/cm2—micro-joules per square centimeter.
It is desirable to effect air sterilization within the room where the germs originate. However, there are safety issues. Keratoconjunctivitis (external idammation of the eye) and erythmea (reddening of the skin) can result from overexposure to W-C and the National Institutes for Occupational Safety and Health (NIOSH) recommends an upper limit on the amount of W-C radiation for the safety of personnel in the room, i.e., 6 μJ/cm2—6 micro-joules per square centimeter over a continuous eight-hour period. Although they may be modified from time to time, the NIOSH guidelines must be considered in the design of fixtures for public spaces.
Because of safety considerations, air sterilization products (e.g., in-duct, ceiling and floor mounted fixtures) generally avoid UV-C radiation into a room and have attempted to confine UV-C radiation to the interior of a closed (i.e., UV-C baffled) chamber, and pass air through the baffled chamber for sterilization.
A significant factor in avoiding excessive UV-C radiation in the lower part of a room, i.e. the part of the room populated by people, is the height at which the UV-C device is located. For example, unbaffled floor and table mounted devices would emit direct UV-C radiation into the lower part of the room. Energy cost considerations have reduced ceiling heights, typically to eight feet, which exacerbates the dilemma of achieving an effective UV-C dose in the upper part of the room without exceeding acceptable limits in the lower part of the room.
Initial efforts to use wall and ceiling pendant UV-C fixtures transmitted an intense UV-C beam at a room height well above the “eye level” of people occupying the room, i.e., generally considered to be approximately 60 inches above the floor. Germ reduction occurred in the air. passing through the beam as a result of convection currents and ventilation systems. While the intensity of the beam was effective in sterilizing the air passing through the beam, the volume and velocity of the air passing through the beam was not controlled and, being thus subject to external forces, such devices have generally been ineffective. In addition, the narrowing of the beam vertically, typically through the use of louvers, wasted most of the UV-C energy making such fixtures highly inefficient.
In an attempt to address this lack of efficacy, Melvin First, Sc. D. of The Harvard School of Public Health has suggested the utilization of a ceiling mounted fan with air intake apertures at the lower end thereof and horizontal air exhaust apertures adjacent the ceiling. As illustrated in FIG. 1 (Prior Art), such a device includes an electric motor 10 with a large impeller 12. As contemplated by Dr. First, air from the room would be drawn upwardly past the motor 10 and a luminaire 14 and laterally exhausted adjacent the ceiling 15. A circular array of unspecified UV-C emitting bulbs 16, stacked three deep was to provide a high intensity UV-C source. This array was to be located circumferentially around the impeller 12 so that air laterally exhausted from the impeller 12 passed by the bulbs 16. Shielding of the lower part of the room from direct irradiation by the UV-C array was to be provided by a laterally extending baffle 18 with the entire structure supported by a number of rods 20.
The device proposed by Dr. First proved impractical for ceilings below about twelve feet because of the large size, i.e., it descended too far vertically into the room (about 24-30″) and the illuminator source would be at eye level for the typical eight foot ceiling. The proposed fixture also laterally occupied too much of the ceiling (about 30-36″ wide) due to the need to laterally extend the baffle limiting the angle of direct radiation into the lower part of the room.
In addition, the use of multiple UV-C sources with a single vertical opening created a steep angle of incidence of the UV-C radiation on the ceiling which would have caused significant UV-C radiation to be reflected downwardly into the lower part of the room resulting in an unacceptable radiation level.
Other disadvantages include the difficulty in accessing and replacing the UV-C lamps because of the large diameter baffle and rod suspension system. Moreover, the placement of the illumination source at the center of the air intake added to the size of the fixture and would have impeded air flow into the air mover, resulting in noise and/or motor inefficiency. Notwithstanding these deficiencies, the amount of air circulated through the device would have represented an improvement over high intensity, densely louvered, narrow beam systems relying on convection currents and room ventilation systems for air mixing.
It is an object of this invention to address the deficiencies of known room air sterilizers and to provide a novel air sterilization and lighting fixture and method. More particularly, it is an object of this invention to provide a novel lighting fixture and method that is effective in providing efficient room lighting as well as safe and effective room air sterilization.
In one aspect, the fixture of present invention uses a novel relatively low intensity and broader UV-C radiation field effective because of the increased time air remains in the field as it is circulated in the room. Because the radiation field is broader, air velocity may be decreased to reduce the noise of the air being moved and drafts to make the fixture acceptable in environments such as hospitals, public libraries, etc.
In another aspect, the compact size of the fixture of the present invention makes it acceptable for use in rooms with relatively low ceilings.
In yet another aspect, the fixture of the present invention limits the visible light emanating from the UV-C source so as to make the fixture acceptable in environments such as hospitals where it is important that the air sterilization avoid interference with the sleep of patients.
In yet still another aspect, the fixture of the present invention is easily adjusted to provide a radiation field appropriate for various ceiling heights.
In a further aspect, the fixture of the present invention provides room illumination without interfering with air flow.
In yet a further aspect, the UV-C source of the present invention is readily accessible for replacement.
In still yet a further aspect, the fixture of the present invention provides remote control of the operation of the fixture and protection of all electrical and electronic components from UV-C radiation.
Many other objects and advantages will be apparent from the following detailed description of preferred embodiments when read in conjunction with the appended drawings.